After their meeting, President Obama and Israeli Prime Minister Benjamin Netanyahu continue to disagree on what should trigger military action against Iran.

Reporting from Washington — President Obama and Israeli Prime Minister Benjamin Netanyahu on Monday sought to offer a united front against Iran's growing nuclear program but appeared to differ on whether a diplomatic solution remains possible or if military action is needed to prevent Tehran from gaining a nuclear bomb.

At a White House meeting, Netanyahu said he reserved the option to launch a unilateral attack on Iran despite Obama's position that more time is needed for stiff economic sanctions and international diplomacy to work.

"When it comes to Israel's security, Israel has the right, the sovereign right, to make its own decisions," Netanyahu told Obama in a brief session with reporters in the Oval Office. "I believe that's why you appreciate, Mr. President, that Israel must reserve the right to defend itself."

The two leaders' last Oval Office meeting, in May, ended in acrimony when Netanyahu lectured Obama before TV cameras on the president's proposal to revive moribund Israeli-Palestinian peace talks.

U.S. officials said late Monday that the two leaders continued to disagree about what should trigger military action against Iran and did not try to resolve their differences in their talks.

They discussed in some detail their timeline for expected developments in Iran's uranium enrichment program, but did not make firm commitments on how their governments would respond, according to people familiar with the talks.

David Makovsky, a Middle East specialist at the Washington Institute for Near East Policy, said that "the net bottom line is that neither side wanted to tie his own hands in committing to any set timetable.... No one was writing the other side a blank check."

Speaking to a pro-Israel audience Monday night, Netanyahu made it clear that he had not yet decided to attack Iran, though he expressed doubts that sanctions or diplomacy would remove the nuclear threat, and voiced impatience. He told the American Israel Public Affairs Committee, or AIPAC, that world powers have tried diplomacy and sanctions for years.

"That hasn't worked, either," he said. "None of us can afford to wait much longer."

Netanyahu said Iran's nuclear program continued "to march forward" but did not say it was "racing," as he has in the past.

Iran has preoccupied Washington in recent days as Obama has reaffirmed his determination to end the presumed nuclear threat in a widely publicized interview and in a speech Sunday at the annual convention of a leading pro-Israel lobbying group, the American Israel Public Affairs Committee.

Though Obama pleased Netanyahu by declaring in his speech that he did not bluff about using military force, the Israeli prime minister's aides said Netanyahu made it clear he remains concerned. Israeli officials say military action is justified if Iran is seen to approach the capability to build a bomb, or if Tehran moves enough of its uranium enrichment program underground to make it less vulnerable to bombing.

The Obama administration says it does not believe military force is necessary unless Iran is building a nuclear bomb. The administration believes Iran would need about a year to develop and build its first nuclear weapon should it decide to do so. Iran says its nuclear program is for peaceful purposes.

A senior White House official said that during the meeting Monday, Netanyahu gave Obama a copy of the biblical Book of Esther, which tells the story — widely considered to be apocryphal — of the foiling of a plot to kill all the Jews in the ancient Persian empire. The official would not say what Netanyahu told Obama about the gift, but did not deny reports in the Israeli media that the prime minister said, "Then, too, they wanted to wipe us out."

As the two leaders debated Iran's nuclear program, a group of world powers continued weighing whether to try to resume negotiations with Iran.

The group — France, Britain, Germany, China, Russia and the United States — has received a letter from Iran indicating a willingness to resume talks, and its members are debating what kind of commitment to require of Tehran. The group wants to ensure that the Iranian negotiators are ready to focus on the nuclear program.

When they last met, in Istanbul in January 2011, the Iranians refused to discuss the nuclear program, and the talks broke down quickly.

Some European governments, notably Britain and France, have grown skeptical of Iran's willingness to negotiate, but there is a widespread feeling in the group that it is worth testing whether recent rounds of sanctions have made Tehran more open to giving ground.

Although Washington has echoed with talk of war in recent days, some observers warned against the U.S. getting involved in another military campaign.

Jeremy Ben-Ami, president of J Street, a liberal pro-Israel group in Washington, said that "a precipitous rush to military action against Iran does not serve the best interests of the United States or Israel."